1. Field of the Invention
The invention relates generally to a device and method to affect aero-dynamic flow over a wing to create desired stall patterns as a means of avoiding adverse pitching moments.
2. Background Art
In general, the stall pattern on an aircraft wing must be tailored to produce the desired pitch characteristics for safe recovery from stall. This is particularly critical for a swept wing aircraft with high lift devices. Quite commonly, as the angle of attack increases, the wing will first stall at the outboard area of the wing, thus destroying the lifting force that is contributed at a more rearward location. This would tend to move the center of lift forward, thus creating a pitching moment that would tend to lift the nose of the aircraft upwardly. This creates an unstable situation where the pitching moment produces an increase in angle of attack. In the case of a piloted airplane, when such a condition is reached, the airplane will pitch towards stall without any pilot input. This unstable condition persists over a range of angle of attack until a stall condition is developed also at a more inboard location, thus eliminating the upward pitching moment and causing the aircraft nose to move downwardly. In general, it is more desirable that the onset of stall occur in a pattern that alleviates abrupt changes in pitching moments and in particular eliminate the abrupt onset of an upward pitching moment and overall creates desired pitch characteristics for safe recovery from stall.
One approach to this problem was incorporated on early DC 9 designs, where the inboard leading edge of the wing was provided with a stall strip that extended along a lower part of the leading edge. In cruise mode, the stagnation point on the leading edge would be slightly above the stall strip so that it would not disturb flow over the wing. However, at higher angles of attack, the stagnation point would move to a location beneath the stall strip so that flow upwardly over the wings would be disturbed in that area so as to promote stall over the inboard area of the wing. However, there was the penalty of increased cruise drag.
A search of the patent literature has disclosed a number of patents which are discussed briefly below. These are the following.
U.S. Pat. No. 2,041,793, Stalker, illustrates a slotted wing configuration where vortex generating devices are located in the slot so as to energize the air and increase lift created by the air passing through the slot.
U.S. Pat. No. 2,549,045, Ashkenas, is directed toward the problem of controlling wingtip stall in airplanes. There is a slot in the tip portion which opens to delay stall.
U.S. Pat. No. 2,694,357, Lee, illustrates the use of vortex generators to energize air going into an inlet so as to maximize recovery of energy.
U.S. Pat. No. 2,885,161, Kerker, et al., shows the use of wing fences to control stall in an aircraft wing.
U.S. Pat No. 3,139,246, Alvarez-Calderon, shows various devices to vary the area, span, camber or thickness of a wing.
U.S. Pat. No. 3,144,220, Kittelson, illustrates a retractable cover members on the upper surface of a wing. These are moved upwardly into the airstream for gust load alleviation so as to destroy lift.
U.S. Pat. No. 3,370,810, Chevell, et al., shows a stall control device for a swept-wing aircraft. There are vortex generating devices positioned on the under surface of the wing. These are intended to avoid blocking of air movement on the upper wing surface while still functioning to create vortex air currents which flow opposite to the direction of the lateral air movement in the boundary layer, thereby countering such movement.
U.S. Pat. No. 3,525,486, Wimpenny, illustrates the use of vortex generators in a blown slot that directs air upwardly over the upper surface of the wing.
U.S. Pat. No. 3,774,867, Quinn, is intended to delay the onset of wing stall. There is a plurality of acoustic generators positioned in the forward portion of the upper surface of the wing.
U.S. Pat. No. 4,032,087, Cleaves, shows a leading edge spoiler which has a generally semi-circular configuration. In one position, the surface of the spoiler lies flush with the aerodynamic surface of the wing, and can be rotated to move into the flow pattern of the wing.
U.S. Pat. No. 4,042,191, Johnson, shows a device to improve the sealing of a gap in a Krueger flap. This is a spring loaded device which is moved by air pressure into sealing engagement.
In view of the foregoing, it is an object of the present invention to provide a apparatus and method for tailoring the stall pattern in a wing so as to avoid adverse pitching moments, this being accomplished in a manner to minimize any drag penalties. Other objects and advantages of present invention will become apparent from the following description.